This invention generally relates to thermal inkjet printing. More particularly, this invention relates to the apparatus and process of manufacturing precise orifices using a graded dielectric material using anisotropic etching and followed by isotropic etching of the graded dielectric material.
Thermal inkjet printers typically have a printhead mounted on a carriage that traverses back and forth across the width of the paper or other medium feeding through the printer. The printhead includes an array of orifices (also called nozzles) which face the paper. Associated with each orifice is a firing chamber. Ink (or another fluid) filled channels feed the firing chamber with ink from a reservoir ink source. Applied individually to addressable resistors, energy heats the ink within the firing chambers causing the ink to bubble and thus expel ink out of the orifice toward the paper. Those skilled in the art will appreciate that other methods of transferring energy to the ink or fluid exist and still fall within the spirit, scope and principle of the present invention. As the ink is expelled, the bubble collapses and more ink fills the channels and firing chambers from the reservoir, allowing for repetition of the ink expulsion.
Current designs of inkjet printheads have problems in their manufacturing, operating life and accuracy in directing the ink onto the paper. Printheads currently produced comprise an inkfeed slot, a barrier interface (The barrier interface channels the ink to the resistor and defines the firing chamber volume. The barrier material is a thick, photosensitive material that is laminated onto the wafer, exposed, developed, and cured), and an orifice plate (The orifice plate is the exit path of the firing chamber. The orifice is typically electroformed with nickel (Ni) and then coated with gold (Au), palladium, or other precious metals for corrosion resistance. The thickness and bore diameter of the orifice plate are controlled to allow repeatable drop ejection when firing.). During manufacturing, aligning the orifice plate requires special precision and special adhesives to attach it to other portions of the printhead. If the orifice plate is warped or if the adhesive does not correctly bond the orifice plate to the barrier interface, poor control of the ink results and the yield or life of the printhead is reduced. If the alignment of the printhead is incorrect or the orifice plate is dimpled (non-uniform in its planarization), the ink will be ejected away from its proper trajectory and the image quality of the printout is reduced. Because the orifice plate is a separate piece, the thickness required to prevent warping or buckling during manufacturing requires the height (related to thickness of the orifice plate) of the orifice bore to be higher than necessary for thermal efficiency. The increased height of the ink in the orifice bore, from the resistor to the orifice plate's outer surface, requires more heating to eject the ink. A related issue is that reproductions that are more accurate require higher resolutions of ink placement onto the medium. Therefore, the amount of ink expelled must be reduced to create a finer dot on the medium. As the quantity of ink expelled becomes smaller, more orifices are required within the printhead to create a given pattern in a single traverse of the printhead over the medium at a fixed print speed. In the past, the lifetime of the printhead was adequate as the printhead was part of a disposable pen that was replaced after the ink supply ran out. User expectations for quality are driving the need to have a long life printhead with multiyear permanence and the present invention helps fulfill this expectation.